For the non-generic enumerable types, only unmapped, assignable types are supported, as AutoMapper will be unable to "guess" what types you're trying to map. As shown in the example above, it's not necessary to explicitly configure list types, only their member types.

Polymorphic element types in collections

Many times, we might have a hierarchy of types in both our source and destination types. AutoMapper supports polymorphic arrays and collections, such that derived source/destination types are used if found.